Puzzling Human Relative Homo Naledi May Have Lived at the Same Time as Our Ancestors

Two views of an adult Homo naledi cranium found in the Lesedi Chamber of the Rising Star cave system in South Africa, where the remains of 15 individuals were discovered in a different cave in 2013.
Two views of an adult Homo naledi cranium found in the Lesedi Chamber of the Rising Star cave system in South Africa, where the remains of 15 individuals were discovered in a different cave in 2013.
Hawks et al. in eLife, 2017

It's tempting to think that evolution works in a straight line, with clearly defined, graduated steps from primitive to modern. We humans are especially prone to telling our own evolutionary story in this manner. Evolution doesn't work that way, though, and we aren’t even the end point of human evolution, but works in progress. (Personally, I hope we are amphibious and have fins in 3 million years. That would be awesome.)

The latest evidence for that essential truth comes from the Rising Star cave system in South Africa, where scientists say Homo naledi, the unusual hominid species they discovered there in 2013, is surprisingly young, living as recently as 236,000 years ago. That means it was one of various hominids wandering the Earth at the same time as the Neanderthals in Europe; the Denisovans in western Asia; the ancestors of the “hobbit,” Homo floresiensis; and, in Africa, potentially alongside the earliest members of our own species, Homo sapiens.

Moreover, the researchers found three more individuals in another chamber in the cave system, one of them with the most complete H. naledi skull discovered yet. (You can see it above.) Today the large team of researchers published a trio of papers documenting their results in the open-access journal eLife.

In 2015, we reported on the initial discovery of 15 sets of hominid remains found in the Dinaledi cave by a team of researchers led by paleoanthropologist Lee Berger. It was an unprecedented bounty of bones. Often, paleoanthropologists are reconstructing human evolutionary history from scant remains—a fragment of skull or jaw bone here, a femur or a finger there. But in the Dinaledi cave, there are at least 1500 bones, and likely a lot more, since only a small fraction of the cave was excavated by a half-dozen archaeologists—all female, all cavers, all slim enough to squeeze through a series of cave tunnels that narrowed to just 7 inches in one spot—who worked in extraordinary conditions to excavate the bones from a pitch-black cave nearly 100 feet beneath the surface.

The ancient creatures were no bigger than the small but formidable women who unearthed them. Slender and about 5 feet tall as adults, they would’ve weighed just under 100 pounds. Their bodies are a fascinating mosaic of primitive and modern: tiny, orange-sized brains housed in skulls with jaws and teeth closer to early Homo; shoulders suited for climbing trees but feet and ankles made for walking; hands potentially capable of making tools, but with fingers well-curved for tightly gripping tree branches.

The discovery made headlines worldwide. Most of us—whether scientist or science nerd—fascinated by the find had one question: How old were they?

DATING THE REMAINS

When H. naledi was first discovered, the researchers deliberately didn’t attempt to answer that question. Determining where a species fits into the evolutionary record based on its morphology is not an unusual approach, but it can also be misleading. In the past 1.5 years, other scientists have proposed ages for H. naledi that range from 100,000 to 2 million years ago.

In one of the current studies, researchers led by James Cook University geologist Paul Dirks conducted six dating tests to narrow the age range, including the paleomagnetic dating of calcite left behind by running water and a chemical analysis of three fossil teeth discovered in the cave using a technique called combined U-series and electron spin resonance (US-ESR) dating. From all the tests, they came up with an age range: they're most likely between 236,000 and 335,000 years old.

As eLife notes in a commentary on the study, “The estimated dates are much more recent than many had predicted, and mean that H. naledi was alive at the same time as the earliest members of our own species—which most likely evolved between 300,000 and 200,000 years ago. These new findings demonstrate why it can be unwise to try to predict the age of a fossil based only on its appearance, and emphasize the importance of dating specimens via independent tests.”

American Museum of Natural History paleoanthropologist Ian Tattersall echoed that sentiment to Mental Floss. “This is an object lesson in trying to date anything by what it looks like,” he says. While he doesn't find the age estimate surprising, he’s less convinced that H. naledi belongs in our Homo genus: “Anything as odd as this is always going to be tough to fit into both a phylogeny and a timescale,” he notes.

Did our ancestors interact with this oddball? We have no idea. But we do know that the picture of human evolution continues to expand in detail and complexity with every discovery like H. naledi.

Bioarchaeologist (and regular Mental Floss contributor) Kristina Killgrove, who teaches biological anthropology, human origins, and evolutionary theory at the University of West Florida, tells us that the long wait for H. naledi dates was “worth it.”

She says, “These dates reveal a much more complicated story of hominin evolution than ever before. We used to think of human evolution as a single lineage—the classic image of the progression from apes to humans. But H. naledi shows that palaeoanthropologists are onto something far more complex—and far more interesting! While these new dates won't make it into textbooks in time for the fall semester, I will certainly be updating my human evolution lectures this summer."

ONE NEW CAVE, THREE NEW BODIES

Whatever we have to learn about this cousin of humanity can only be helped by the other discovery reported today in eLife: 133 bones from three likely H. naledi individuals—two adults and one child—found in another cave in the Rising Star system. First spotted in 2013 by cavers, the bones were unearthed in three locations in a cave the researchers coined Lesedi. The two caves are found at the same depth, but they’re not directly connected.

As with the first expedition into the Dinaledi cave, the working conditions for the researchers weren’t easy: Wits University archaeologist Marina Elliott, who led the intrepid team of “underground astronauts” who excavated both sites, told National Geographic that while the Lesedi cave was slightly easier to reach than Dinaledi, she still had to excavate one set of remains from a 2-foot-wide alcove while laying on her chest, her shoulders pinned between rocks. “It’s extremely physically difficult,” she said. “I’ve tried to do a lot of yoga to get myself to be able to do it.”

Elliott would probably say it was worth it, though; the remains she excavated in that location yielded the most complete H. naledi skull so far discovered. Dubbed Neo (after the Setswana word for "a gift," not the The Matrix character), this adult has a larger skull—and therefore a larger brain capacity—than the other specimens so far discovered, but it falls within an expected range.

ARE THESE BURIALS OF A SORT?

One of the most contentious theories Berger and the team proposed when the first H. naledi fossils were discovered was that these bodies had been intentionally placed in the cave in some sort of death ritual. Berger and John Hawks, a paleoanthropologist at the University of Wisconsin, revisit that theory in the third paper published in eLife. They point out that the caves are difficult to access and aren’t obvious “death traps” that individuals could’ve accidentally fallen into. Nor did the remains show any signs of mass death, having been fed upon by carnivores or scavengers, or of having been flushed into the caves by a water system.

So how did they get there?

The researchers write, “We propose that funerary caching by H. naledi is a reasonable explanation for the presence of remains in the Dinaledi and Lesedi Chambers. Mortuary behaviors, while culturally diverse, are universal among modern human cultural groups. Such behaviors are not seen in living non-human primates or in other social mammals, but many social mammals exhibit signs of grief, distress, or other emotional response when other individuals within their social group die.”

They say that while there’s no evidence of symbolic thinking among H. naledi, such sophisticated thought isn’t necessarily a requirement for a death ritual. The “physical and social effects of the deaths of group members” could have been motivation enough.

“Such behavior may have many different motivations, from the removal of decaying bodies from habitation areas, to the prevention of scavenger activity, to social bonding, which are not mutually exclusive,” they note. “We suggest only that such cultural behavior may have been within the capabilities of a species that otherwise presents every appearance of technical and subsistence strategies that were common across the genus Homo.”

10 Products for a Better Night's Sleep

Amazon/Comfort Spaces
Amazon/Comfort Spaces

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Everlasting Comfort Knee Pillow
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White noise machines: They’re not just for babies! This Letsfit model—which is rated 4.7 out of five with nearly 3500 reviews—has 14 potential sleep soundtracks, including three white noise tracks, to better block out everything from sirens to birds that chirp enthusiastically at dawn (although there’s also a birds track, if that’s your thing). It also has a timer function and a night light.

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5. Philips SmartSleep Wake-Up Light; $200

Philips SmartSleep Wake-Up Light
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If you’re looking for an alarm clock with even more features, Philips’s SmartSleep Wake-Up Light is smartphone-enabled and equipped with an AmbiTrack sensor, which tracks things like bedroom temperature, humidity, and light levels, then gives recommendations for how you can get a better night’s rest.

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Stratus sheets from Slumber Cloud.
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This pillow—which has a 4.5-star rating on Amazon—is filled with memory foam scraps and microfiber, and comes with an extra half-pound of fill so you can add, or subtract, the amount in the pillow for ultimate comfort. As a bonus, the pillows are hypoallergenic, mite-resistant, and washable.

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9. Baloo Weighted Blanket; $149-$169

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Though the science is still out on weighted blankets, some people swear by them. Wirecutter named this Baloo blanket the best, not in small part because, unlike many weighted blankets, it’s machine-washable and -dryable. It’s currently available in 12-pound ($149) twin size and 20-pound ($169) queen size. It’s rated 4.7 out of five stars on Amazon, with one reviewer reporting that “when it's spread out over you it just feels like a comfy, snuggly hug for your whole body … I've found it super relaxing for falling asleep the last few nights, and it looks nice on the end of the bed, too.” 

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10. Philips Smartsleep Snoring Relief Band; $200

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Few things can disturb your slumber—and that of the ones you love—like loudly sawing logs. Philips’s Smartsleep Snoring Relief Band is designed for people who snore when they’re sleeping on their backs, and according to the company, 86 percent of people who used the band reported reduced snoring after a month. The device wraps around the torso and is equipped with a sensor that delivers vibrations if it detects you moving to sleep on your back; those vibrations stop when you roll onto your side. The next day, you can see how many hours you spent in bed, how many of those hours you spent on your back, and your response rate to the vibrations. The sensor has an algorithm that notes your response rate and tweaks the intensity of vibrations based on that. “This device works exactly as advertised,” one Amazon reviewer wrote. “I’d say it’s perfect.”

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This Football-Sized Fossil Egg is the First Found in Antarctica, and It May Have Belonged to a Mosasaur

An artist’s interpretation of the birth of a baby mosasaur.
An artist’s interpretation of the birth of a baby mosasaur.
Francisco Hueichaleo, 2020

In 2011, Chilean scientists discovered a football-sized fossil off the coast of Seymour Island, near the northern tip of the Antarctic Peninsula. Though they didn’t know what it was at the time—and simply called it “The Thing”—new research shows that not only is it the first fossil egg ever found in Antarctica, it’s also the largest soft-shelled egg ever found anywhere.

In a study published today in the science journal Nature, researchers from the University of Texas at Austin and the University of Chile dated the nearshore rock formation where the fossil egg was found to be from the Late Cretaceous period—about 68 million years ago—and measured the fossil itself to be roughly 11.4 inches by 7.9 inches (29 centimeters by 20 centimeters). This empty, partially collapsed egg is smaller only than that of the elephant bird, an extinct, flightless species from Madagascar whose eggs averaged about 12 inches by 8 inches.

giant fossil egg from antarctica
A side view of the fossil egg.
Legendre et al. (2020)

But beyond their size, the eggs don’t have much in common; an elephant bird egg is about five times thicker than this fossil egg, and its hard shell has distinct pores and a prismatic layer that the fossil egg lacks. In other words, an elephant bird egg resembles a giant chicken egg. (And giant is no exaggeration—an elephant bird egg could hold the contents of about 150 chicken eggs.)

elephant bird egg next to a chicken egg
An elephant bird egg next to a chicken egg (and a man's head), to put it in perspective.
Oli Scarff/Getty Images

With its soft shell and oblong shape, the new fossil egg, from the new taxon Antarcticoolithus bradyi, is more similar to a lizard or snake egg, which suggests it could’ve been laid by a large reptile. To test that theory, the researchers compared it to the egg traits of 259 species of lepidosaurs—a subclass of reptile that includes snakes and lizards—and surmised that the egg-layer may have been a marine reptile that measured roughly 23 feet (7 meters) or longer.

The researchers believe this mystery mother might have been a mosasaur, a type of large marine lepidosaur whose remains have also been discovered in the area. During the Late Cretaceous period, mosasaurs were among the most fearsome predators in the ocean. They had strong flippers and sharp teeth, and some species grew as long as 50 feet (though that’s still a good 10 feet shorter than the fictional mosasaur depicted in 2015’s Jurassic World). Fossilized contents of their stomachs show they feasted on a variety of wildlife, including fish, seabirds, turtles, plesiosaurs, and more—one mosasaur had even eaten a few other mosasaurs. And although mosasaurs did live in Antarctica, the continent during the Late Cretaceous period looked nothing like its current frigid landscape.

“Antarctica was rich in life,” Dr. Julia Clarke, a professor in UT Austin’s Department of Geological Sciences and co-author of the study, tells Mental Floss. “Temperate forests diverse in plant species covered exposed land. Giant marine reptiles and much smaller coiled ammonites and relatives of living birds hunted in the seas, while on land, mid-sized non-avian dinosaurs ambled.”

mosasaur birth and egg
The egg looks a lot smaller when you compare it to a full-grown mosasaur.
Francisco Hueichaleo, 2020

Since scientists have uncovered the remains of mosasaurs and plesiosaurs of all ages in the rock formation where the fossil egg was found, some think it may have been a popular place for creatures to hatch and raise their young.

“Many authors have hypothesized that this was sort of a nursery site with shallow protected water, a cove environment where the young ones would have had a quiet setting to grow up,” Lucas Legendre, a postdoctoral researcher and the lead author of the study, said in a press release.

If the fossil egg really did belong to a mosasaur, it could alter our understanding of how mosasaurs gave birth. In South Dakota during the 1990s, scientists unearthed the skeleton of a lizard-like mosasaur called a Plioplatecarpus with five unborn offspring preserved in its abdomen. Because they weren’t in eggs, it was generally thought that mosasaurs gave birth to live young. The existence of Antarcticoolithus bradyi, however, suggests the possibility that some mosasaurs laid soft-shelled eggs that hatched immediately after.

According to Clarke, the discovery of the fossil egg is especially exciting because it demonstrates “how much we have yet to learn about the evolution of eggs, from the first egg-layers that moved away from water to the immense diversity of eggs and reproductive strategies we see today.”